Neomycin and polymyxin are effective in killing gram-negative bacteria, while bacitracin targets gram-positive bacteria; hence, this 'triple antibiotic' ointment covers for a wide range of bacteria which may infect wounds.
However, these antibiotics are generally only used topically, because they are known for causing serious side effects (such as nephrotoxicity) when used parenterally. Even when used topically, the antibiotic ointment may cause side effects; in particular, neomycin is well-known for causing allergic reactions such as allergic contact dermatitis. Commonly, though harmlessly, Neosporin tends to exaggerate the pain of abrasions and external injuries.
Neosporin is also used as a brand name for several other U.S. products that do not contain neomycin.
Pfizer also produces a related mixture of bacitracin and polymyxin, branded Polysporin. Because neomycin is not included in Polysporin, Polysporin may be safely used in individuals with allergies to neomycin. Recently, Pfizer also introduced "Neosporin + Pain Relief," ointment and cream, containing pramoxine, a topical analgesic. In addition to its pain relieving properties, the cream (which omits the bacitracin zinc, as it is not stable in the cream base) appears useful in individuals sensitive to bacitracin, as well as those sensitive to zinc. The "Maximum Strength Neosporin + Pain Relief" formula contains bacitracin, neomycin, polymyxin B, and pramoxine HCl.
In Canada and Australia, the Neosporin brand is not sold at all, but Polysporin is sold in several varieties. The "original" ointments contain polymyxin B and bacitracin, while the creams and eye/ear drops contain polymyxin B and gramicidin. A "triple" ointment is also available containing all three of the above antibiotics.
Although available in the US, Canada, India and numerous other countries, Neosporin is not available over the counter in the UK